1. Field of the Invention
The present invention relates in general to conduit bending, and specifically relates to an apparatus which is attached to a section of conduit to be bent by a conventional conduit bending tool to provide a visual indication that a bend is remaining within a referenced plane and is not being skewed or forming a dog-leg.
2. Description of the Prior Art
In the building trades, there is frequently a need for bent tubing or conduit to carry utilities such as electrical wiring along the contours and shapes of a building. Multiple bends of a single section of conduit are frequently required to avoid a particular obstacle. A generally U-shaped or "saddle" bend is commonly made in the conduit to avoid obstacles impeding a straight run of conduit. It is clearly more advantageous to bend the conduit at the construction site, so that bends of various angles to fit the particular installation or application may be made with greater flexibility in surmounting unforseen obstacles.
Conventional bending machines exist which may be used to form such bends with great angular and planar precision, but many of these machines are very large and impracticable for use at a construction site. Other types of conventional bending devices have been devised which are much simpler and smaller than the heavy-duty machines and which may easily be transported about a construction site so that bending of tubes may be done on-site, but these smaller machines often produce inferior bends if not used skillfully.
The tube bending apparatus disclosed in Gardner, U.S. Pat. No. 3,465,560, is a relatively large and immobile machine which provides superior bends because it prevents re-positioning of the conduit partway through a bending operation. Those skilled in the art will recognize that repositioning a conduit partway through a bending operation greatly increases the chance of displacement of the bending plane midway through the bend. The result of displacement of the bending plane is a twisted bend section or a "dog-leg", which renders the tube useless.
The patent to Miller, U.S. Pat. No. 3,396,565 discloses a tubing bending apparatus which is relatively portable but provides no means for preventing dog-legs. A clinometer is frictionally attached to the conduit by means of a releasable clamp and provides an indication as to the degree of bend of a conduit in the machine. However, the clinometer is only suitable for indicating the degree of bend and provides no indication of whether a dog-leg exists in a particular section of pipe in the machine. The Miller apparatus appears to prevent dog-legs by moving the conduit intermittently through the bending device with a feeding mechanism which advances the conduit in step-by-step increments. A pair of clamps alternatively grip and advance the pipe through the apparatus thereby preventing displacement of the bending plane. The Miller apparatus, however, is large, bulky, and expensive due to the intricate clamping mechanism and hydraulics.
Other means have been proposed for improving conventional on-site tube bending devices by including an angle indicating means. U.S. Pat. No. 2,932,225 to Gardner discloses a bending indicator provided with spirit levels which may be attached to the bending apparatus, thereby enabling the workman to determine the degree of bend without the use of other instruments. Since the Gardner device is attached to the body of the bending apparatus, rather than to the conduit, the apparatus does not provide an indication with respect to the bending plane of the conduit and is useful only for providing an indication of the degree of bend of the apparatus.